Fastening products such as slider fasteners, snap buttons, and buckles have been generally used until now as means for coupling two members. Various fastening members such as fastener elements are disposed in fastening products such as slider fasteners, and many fastening members are injection-molded of a synthetic resin in that the fastening members are inexpensive and can easily correspond to various shapes. However, such fastening members of a synthetic resin generally lack in glossiness, and thus a high-grade sense cannot be realized in the fastening products.
Meanwhile, when glossiness is given to a fastening product to show a high-grade sense, a fastening member, for example, such as a fastener element may be formed of a metal such as copper or aluminum. However, manufacturing costs for a fastening product having such a metallic fastening member are high as compared with a case of using a fastening member of a synthetic resin, and a manufacturing method thereof also requires a plurality of processes and thus is complex.
Further, a metallic fastening member is heavier than a fastening member of a synthetic resin, and thus when a fastening product is attached to an end product such as clothes or a bag, weight of the end product itself increases. Thus, for example, in a product pursuing light weight, even when glossiness is to be given to a fastening product, a synthetic resin fastening member cannot but be selected in terms of costs and weight in some cases.
In order to solve such a problem, for example, Japanese Patent Application Laid-Open No. 58-58003 (Patent Document 1) discloses a slide fastener where at least one of a slider and a fastener element is formed of a thermoplastic synthetic resin mixed with metal foil containing aluminum. In this case, Patent Document 1 describes that it is preferable that the metal foil mixed with the synthetic resin has a size of 200 μm×280 μm or a size of 100 μm×140 μm.
In this way, as a slider or a fastener element are injection-molded of a synthetic resin mixed with metal foil having the above-described size, glossiness may be given to the slider or the fastener element to improve an appearance quality (aesthetic sense) of the slide fastener. Further, according to Patent Document 1, through the mixing of the metal foil, the slider or the fastener element is formed to be firm and an impact-resistant force increases.
However, for example, the specification of Japanese Patent No. 3994245 (Patent Document 2) discloses an aluminum flake which is controlled to have a particle size in a predetermined range as an invention relating to aluminum metal foil (aluminum flakes) mixed with a synthetic resin during injection molding.
For example, when a synthetic resin mixed with aluminum flakes having a relatively large size (particle size) is injection-molded, a flow of a melted resin in a cavity of a mold deteriorates due to the mixing of the aluminum flakes or stains are caused in the flow of the melted resin, and thus a mixing ratio of the metal foil may be partially lower in a formed product. As a result, in the formed product, as the mixing ratio of the metal foil is low, a partially discolored weld mark may be formed and thus may cause an appearance defect of the formed product.
In regard to the appearance defect problem, the aluminum flake disclosed in Patent Document 2 is controlled such that an average particle diameter thereof by a laser diffraction method is 2 to 8 μm and particles having a size of not less than 10 μm occupies not more than 5.0 wt %. Further, the aluminum flake is controlled such that an average thickness thereof is 0.1 to 0.6 μm, and a linear gradient n of the particle distribution is not less than 2.1.
According to Patent Document 2, for example, when mixed with a synthetic resin such as polyethylene to be injection-molded, the aluminum flakes whose particle size is controlled to the above-described range may restrain a weld mark from being generated in the formed product to a degree where the weld mark cannot be visually recognized or does not lower a product value.
Thus, according to Patent Document 2, the aluminum flakes whose particle size is controlled to the above-described range are properly used when a formed product including an optical device such as a camera or a video camera, an acoustic device such as a radio cassette or a CD player, an OA device such as a PC or a display, and interior/exterior equipment of a vehicle or a motor cycle is injection-molded.